MDT-0123 Japan Study

Inclusion Criteria: * Requirement for bone fusion via consecutive 2-level spinal fusion due to disc degeneration or spinal deformity in the lumbosacral spine (L2-S1) * Symptomatic degenerative lesions from L2 to S1 confirmed by imaging (MRI or myelography within 12 months prior to enrollment) with neurological symptoms due to nerve root compression, including radiating pain, sensory disturbance, numbness, weakness, or neurogenic claudication * Degenerative disc disease with discogenic back pain, with or without leg pain, supported by clinical history and radiographic findings (e.g., CT, MRI, X-ray), with at least one of the following: instability (angular motion ≥5° and/or translation ≥4 mm), osteophyte formation, decreased intervertebral disc height, ligamentous thickening, disc degeneration or herniation, or facet joint degeneration * Preoperative Oswestry Disability Index (ODI) score ≥35% * Skeletally mature * Age 18 to 80 years at the time of surgery * Failure to respond to at least 3 months of non-operative treatment (e.g., bed rest, physical therapy, medication, nerve block, manipulation, or transcutaneous electrical nerve stimulation) * Ability to provide written informed consent after receiving adequate explanation of the study Exclusion Criteria: * Prior spinal surgery at the target or adjacent intervertebral level, except for decompression procedures such as discectomy * Inability to complete both investigational device implantation and posterior fixation in a single procedure * Expected total rhBMP-2 dose greater than 12 mg * Planned use of an internal or external bone growth stimulator * Osteoporosis defined as T-score ≤ -2.5 within 12 months with fragility fracture * Body mass index (BMI) \>40 * Active malignancy * Active local or systemic infection * Use of bone formation promoting agents within 12 months prior to implantation * Use of medications that may interfere with bone or soft tissue healing within 30 days prior to implantation, including corticosteroids, antitumor agents, or immunosuppressants * History of autoimmune diseases affecting bone metabolism or the spine, including ankylosing spondylitis, inflammatory bowel disease, or rheumatoid arthritis * History of endocrine or metabolic disorders affecting bone formation, including Paget's disease or osteodystrophy * Prior exposure to modified proteins used for bone formation * Known hypersensitivity or allergy to device materials or related substances, including titanium, collagen, or protein-based products * History of severe allergic reactions such as anaphylaxis * Mental or psychiatric conditions that may interfere with study participation * Participation in another clinical study within 3 months or planned participation during this study period * Inability or unwillingness to use appropriate contraception during the study period and for 12 months after implantation * Presence of spinal tumors in adjacent vertebrae * Existing or planned implantation of non-study implants in the lumbosacral spine * Medical conditions that could interfere with evaluation of safety or effectiveness, including significant vascular or anatomical abnormalities * Contraindications to MRI * Smoking within 12 weeks prior to implantation or unwillingness to abstain during the study period * Alcohol or substance abuse * Any condition that, in the investigator's judgment, makes the subject unsuitable for the study